Kneading apparatus and method for kneading rubber-based composition using the same

ABSTRACT

A kneading apparatus includes a barrel having a cylindrical chamber; a screw assembly rotating in the chamber so that a material to be kneaded is extruded in the axial direction by the rotation, the screw assembly including a screw section having helical blades and a kneading blade section in order to allow the material to flow into the clearance between the inner wall of the chamber and the kneading blade section, and to apply shearing forces to the material; a metering feeder for feeding the material at a substantially constant volumetric or gravimetric rate into the chamber; an injecting device for injecting a heat-removing medium into the chamber; and a discharging device for separating the heat-removing medium from the material and discharging the heat-removing medium from the chamber. A kneading method using the kneading apparatus is also disclosed.

The present application is a continuation of U.S. application Ser. No.11/249,633, filed on Oct. 14, 2005 and now abandoned, which is acontinuation of U.S. application Ser. No. 10/123,253, filed on Apr. 17,2002 now U.S. Pat. No. 7,004,616, which claims priority under 35 U.S.C.§119 to Japanese application 2001-127684, filed on Apr. 25, 2001, thecontents of which are hereby incorporated by reference in theirentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to kneading apparatuses. Moreparticularly, the invention relates to a kneading apparatus used formasticating rubber and for kneading a rubber-based composition in whichrubber and various compounding ingredients are mixed, and to a kneadingmethod using the kneading apparatus.

2. Description of the Related Art

In order to produce a kneaded rubber-based composition including rubberand various compounding ingredients, a batch process is often used, inwhich predetermined amounts of raw materials are intermittently kneaded.However, in order to improve productivity, a method for continuouslykneading a rubber-based composition has also been disclosed (JapaneseUnexamined Patent Application Publication No. 11-262945). In such amethod, a twin-screw extruder, which is a typical kneader forrubber-based compositions, is used. The twin-screw extruder is providedwith a rubber feed port, and a rubber-feeding extruder is furtherconnected thereto. Continuous kneading is performed by the twin-screwextruder while continuously feeding the rubber-based composition.

However, the continuous kneading method according to Japanese UnexaminedPatent Application Publication No. 11-262945 is not suitable forrubber-based compositions having high viscosities, and as described inExample 1 in the patent application publication, the method aims tocontinuously knead a rubber-based composition having a low viscosity,e.g., a Mooney viscosity (100° C.) of approximately 47.

When a rubber-based composition having a high viscosity, e.g., a Mooneyviscosity (100° C.) of more than 100, is kneaded, such as in the case ofa composition in which natural rubber as a major ingredient and 30 partsor more of carbon are mixed, kneading treatment is performed to improvethe dispersion of various compounding ingredients and also to decreasethe viscosity of the rubber-based composition to a viscosity suitablefor later processes, such as extrusion molding. The viscosity isdecreased because rubber molecular chains are cut due to mechanicalshearing. However, heat generation due to mechanical shearing forcesapplied to rubber increases as the viscosity is increased, and if thetemperature becomes excessively high, the physical properties of therubber are changed, thereby degrading the performance of the rubber. Ingeneral, if the temperature exceeds 160° C., the performance of therubber is hindered. Because of the high viscosity of rubber, the cuttingeffect of molecular chains due to mechanical shearing is easilydemonstrated when kneading is performed at lower temperatures, which isalso advantageous in terms of kneading efficiency. In practice, when arubber-based composition with a high viscosity is kneaded, it isextremely difficult to achieve a predetermined decrease in viscosity anda predetermined degree of dispersion of the compounding ingredientswhile the materials to be kneaded are maintained at low temperatures soas not to exceed the temperature range required to ensure the physicalproperties of the rubber. Therefore, kneading is performed by abatch-type kneader. When the temperature reaches approximately 160° C.during kneading, the materials to be kneaded are recovered from thekneader and cooled to ambient temperature after sheet forming isperformed. Kneading is performed again in order to decrease theviscosity. Such a rekneading step is referred to as a remill step.

However, when a rubber-based composition having a high viscosity iskneaded by the method described above, the remill step is usuallyrepeated several times until the predetermined viscosity is achieved.Remilling is often performed approximately five times. Consequently, theproductivity inevitably decreases due to repeated kneading by thebatch-type kneader and cooling, and since thermal hysteresis then takesplace, alteration of the rubber easily occurs.

SUMMARY OF THE INVENTION

The objects of the present invention are to provide a kneading apparatusfor rubber-based compositions having high viscosities in whichcontinuous kneading treatment can be performed without repeatedremilling, thus greatly improving productivity, and to provide akneading method using the kneading apparatus.

In one aspect of the present invention, a kneading apparatus includes abarrel having a cylindrical chamber; a screw assembly rotating in thechamber so that a material to be kneaded is extruded in the axialdirection by the rotation, the screw assembly including a screw sectionhaving helical blades and a kneading blade section in order to allow thematerial to be kneaded to flow into the clearance between the inner wallof the chamber and a kneading blade of the kneading blade section, andto apply shearing forces to the material to be kneaded; a meteringfeeder for feeding the material to be kneaded at a substantiallyconstant volumetric rate or at a substantially constant gravimetric ratefrom a feed port provided on the barrel into the chamber; an injectingdevice provided on the barrel for injecting a heat-removing medium intothe chamber; and a discharging device for separating the heat-removingmedium which has been injected into the chamber by the injecting deviceand mixed with the material to be kneaded from the material to bekneaded, and discharging the heat-removing medium from the chamber.

In the structure described above, continuous kneading can be performedwhile feeding the material to be kneaded to the kneading extruder at aconstant rate, and injection of the heat-removing medium into thechamber and the discharge of the heat-removing medium from the chambercan also be performed continuously. That is, the heat-removing mediumremoves heat while being mixed with and brought into sufficient contactwith the material to be kneaded which generates heat due to kneading,and the heat-removing medium is discharged from the chamber. Therefore,heat-removing treatment of the material to be kneaded can be efficientlyperformed during kneading.

Accordingly, by using an apparatus having the structure described above,it is possible to perform kneading treatment in which the viscosity isdecreased to a predetermined level without having a high-temperaturestate even when the material to be kneaded is a rubber-based compositionand the heat-removing medium is water. That is, with respect to arubber-based composition having a high viscosity, continuous kneadingtreatment can be performed without repeated remilling, resulting in agreat improvement in productivity. Additionally, in such a structure,since the positions and numbers of the injecting devices (injectingdevices for heat-removing medium) and the discharging devices(discharging devices for heat-removing medium), as well as the amount ofinjection, can be selected in any given manner, it is possible to adjustthe cooling capacity appropriately depending on the characteristics ofthe rubber-based composition and the kneading extruder.

For example, when a rubber-based composition is fed at a hightemperature or when the temperature of a rubber-based composition isincreased while being passed through the rubber metering feeder and thekneading effect is decreased, the rubber-based composition is broughtinto contact with injected water in the kneading extruder so that therubber-based composition is cooled primarily by the sensible heat of thewater, and the water used for cooling is discharged through thedischarging device, such as a slit, provided on the barrel, and thuscooling of the rubber-based composition is accelerated, and then therubber-based composition may be subjected to the subsequent kneadingstep.

Additionally, Japanese Unexamined Patent Application Publication No.7-227845 discloses a batch-type kneader in which water is added whenkneading is performed. The publication relates to a method forreutilizing unvulcanized foamed rubber used for tires which has failedto meet the standards with respect to the expansion rate, dimensionalaccuracy, etc., and a foaming agent is decomposed and eliminated bykneading the unvulcanized foamed rubber mixed with a small amount ofwater in a batch-type hermetically closed mixer. That is, there aredifferences in the problems to be solved and the features between thepresent invention and Japanese Unexamined Patent Application PublicationNo. 7-227845.

Preferably, in the kneading apparatus of the present invention describedabove, the discharging device for discharging the heat-removing mediumincludes a vacuum pump connected to the chamber for evacuating thechamber in the region in which the screw section is placed.

In such a structure, when water is used as the heat-removing medium, thewater extruded together with the rubber-based composition to the screwsection under reduced pressure is vaporized and sucked out by the vacuumpump, and just water Can be eliminated efficiently without dischargingthe material to be kneaded from the chamber. That is, when water isseparated from the material to be kneaded, the water absorbs heat ofvaporization from the material to be kneaded, and since the heat ofvaporization of water is significantly larger than thetemperature-raising heat of water, it is possible to provide anefficient cooling means with a small amount of water. Since water isremoved from the material to be kneaded by vaporization, water does notsubstantially remain in the kneaded material, and thus a dischargingdevice with satisfactory dewaterability can be provided. Since the screwsection which is interposed between two kneading blade sections isevacuated, the sealing effect can be displayed due to the material to bekneaded which is loaded in the kneading blade sections, and it ispossible to provide a reduced pressure space sufficient for vaporizingwater.

Additionally, in the present invention, the heat-removing medium is notlimited to water.

Preferably, in the kneading apparatus of the present invention describedabove, the discharging device for the heat-removing medium includes aslit formed in the barrel in the region in which the screw sectionplaced.

In such a structure, even when water is used as the heat-removing mediumand a large amount of cooling water is required, dewatering can beperformed efficiently. A dewatering device can be produced with a simpleconstruction. Even if the rubber-based composition to be fed into thekneading extruder is in a high temperature state, it is possible to coolthe composition efficiently before kneading treatment is performed.

Preferably, the kneading apparatus of the present invention furtherincludes at least one gap-adjusting device provided at the outlet of thekneading blade section so as to sandwich the screw assembly, thegap-adjusting device being capable of adjusting a gap formed between thescrew assembly and the gap-adjusting device.

In such a structure, by changing the gap at the outlet of the kneadingblade section, i.e., by changing the area through which the material tobe kneaded passes, the extruded material to be kneaded is squeezed andthe flow resistance of the material to be kneaded is changed, and thusthe material residence time in the kneading extruder can be adjusted.That is, it is possible to adjust the filling factor of the material tobe kneaded in the kneading blade section, and desired kneadingconditions can be easily adjusted.

Preferably, in the kneading apparatus of the present invention describedabove, the metering feeder is either a gear pump or a screw extruderconnected to the feed port provided on the barrel.

In such a structure, by using the gear pump or screw extruder as themetering feeder, it is possible to stably feed the material to bekneaded to the kneading extruder at a constant rate. Thereby, variationsin the quality of the kneaded product can be suppressed. The form of thematerial to be kneaded is not particularly limited, and various forms,such as blocks, veils, sheets, and ribbons, may be selected.

Preferably, the kneading apparatus of the present invention furtherincludes a temperature-measuring section for measuring the temperatureof the material to be kneaded in the chamber, and a control section forcontrolling the amount of the heat-removing medium to be injected intothe chamber or the speed of rotation of the screw assembly based on themeasured temperature.

In such a structure, it is possible to change the driving conditions andthe cooling conditions of the kneading extruder depending on thetemperature of the material to be kneaded during kneading. That is,although the heat-generating state always changes during kneading, it ispossible to change the cooling conditions and the speed of rotationappropriately so that the optimum kneading conditions can be achieved.

In another aspect of the present invention, a method for kneading arubber-based composition including rubber and compounding ingredientsusing the kneading apparatus described above includes: a feeding step offeeding the rubber-based composition into the chamber at a substantiallyconstant volumetric rate or at a substantially constant gravimetric rateby the metering feeder; a kneading step of allowing the rubber-basedcomposition to flow into the clearance between the inner wall of thechamber and the kneading blade section and moving the rubber-basedcomposition in the chamber while mixing and dispersing the rubber-basedcomposition by means of shearing forces; a mixing step of injecting aheat-removing medium into the chamber by the injecting device and mixingthe rubber-based composition with the heat-removing medium before orduring kneading; and a discharging step of separating the heat-removingmedium which has been injected into the chamber by the injecting deviceand mixed with the rubber-based composition from the rubber-basedcomposition and discharging the heat-removing medium by the dischargingdevice.

In such a method, a rubber-based composition can be continuously kneadedby the kneading extruder and heat removal can be simultaneouslyperformed during kneading. Consequently, even in the case of arubber-based composition having a high viscosity, kneading treatment canbe performed so that the viscosity is decreased to a predetermined levelwithout having a high temperature state. That is, a rubber-basedcomposition having a high viscosity can be continuously kneaded withoutrepeated remilling, resulting in a great improvement in productivity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of a kneading apparatus forrubber-based compositions, viewed from a side, in a first embodiment ofthe present invention;

FIG. 2 is a sectional view taken along the line II-II of FIG. 1;

FIG. 3 is a schematic sectional view of a kneading apparatus forrubber-based compositions, viewed from a side, in a second embodiment ofthe present invention;

FIG. 4 is a schematic sectional view which shows a part of a kneadingapparatus for rubber-based compositions in a third embodiment of thepresent invention;

FIG. 5 is a schematic diagram of a gate device at a cross sectionperpendicular to the shafts of the screw assembly;

FIG. 6 is a schematic diagram showing a kneading apparatus forrubber-based compositions in a fourth embodiment of the presentinvention;

FIG. 7 is a schematic diagram showing a modified kneading apparatus forrubber-based compositions; and

FIG. 8 is a schematic diagram showing another modified kneadingapparatus for rubber-based compositions.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of the present invention will be described withreference to FIG. 1. FIG. 1 is a schematic sectional view of a kneadingapparatus for rubber-based compositions, viewed from a side, in thisembodiment. The kneading apparatus includes a co-rotating intermeshingtwin-screw kneading extruder 1. A rubber metering feeder 2 is connectedto the twin-screw kneading extruder 1, and injection pumps 3 and 4constituting injecting devices and vacuum pumps 5 and 6 constitutingdischarging devices are also connected thereto. The front end of thetwin-screw kneading extruder 1 is exposed to air, and the rubber-basedcomposition is discharged as a lump.

The twin-screw kneading extruder 1 includes a screw assembly 7 composedof a pair of screws, and a barrel 9 including a cylindrical chamber 8 inwhich the screws rotate. The shafts of the screws are parallel to eachother and completely overlap in the side view shown in FIG. 1. Amaterial to be kneaded is extruded in the axial direction by therotation of each screw. The screw assembly 7 alternately includes screwsections 7 a (first), 7 c (second), 7 e (third), and 7 g (fourth) havinghelical blades and kneading blade sections 7 b (first), 7 d (second), 7f (third), and 7 h (fourth) for allowing the material to be kneaded toflow in the clearance between the inner wall of the chamber 8 and thekneading blade sections and for applying shearing forces to the materialto be kneaded. Both screws are connected to a driving device (not shownin the drawing) and are rotated by the driving device.

The helical blades in each screw section are formed along theperipheries of the individual screw shafts so as to extend in the axialdirection. The tops of the helical blades are positioned at the samedistance from the centers of the shafts of the screws. The pair ofscrews having the helical blades formed in the same direction rotate inthe same direction, and thereby the material to be kneaded is movedrightward in FIG. 1. The helical pitches of the helical blades providedin the screw sections are not necessarily the same, and the helicalblades may have densely pitched areas and sparsely pitched areas. Forexample, as will be described below, when water is injected for coolingthe material to be kneaded, the helical blades located downstream in theextrusion process may be densely pitched so that the material to bekneaded is subjected to a filling and compressing action, thus providinga dewatering function. When a portion of the chamber 8 is evacuated bysuction, the helical blades located in the areas adjacent to the spaceto be evacuated by suction may be densely pitched, or helical blades orsheets effective in blocking the material to be kneaded may be placed sothat the areas adjacent to the space to be evacuated by suction arefilled with the material to be kneaded, thereby displaying a sealingeffect. Alternatively, reverse flighted screws, which are helical bladesformed in the opposite direction, may be partially provided, or rotorsor kneading disks as return segments (L segments) in which blades in theopposite direction are formed may be partially provided so that thefilling factor of the material to be kneaded is increased, therebyproducing a pressurized state.

In each kneading blade section placed between the screw sections, threekneading blades are provided along the periphery of each screw with anangle of 120° therebetween, each kneading blade having a cross sectionsuitable for kneading, i.e., having a shape such that a bite angle tothe material to be kneaded is created. Each kneading blade is helicallyand slowly wound about the screw shaft extending in the axial direction.At the midpoint of each kneading blade section, the helical direction isreversed. Herein, the helical direction of the kneading blades locatedupstream in the extrusion process is defined as a normal direction andthe helical direction of the kneading blades located downstream isdefined as an opposite direction. The materials to be kneaded aretransported to the kneading blade section composed of the kneadingblades having the normal and opposite helical directions fill thekneading blade section to await kneading. Kneading is performed so thatthe material to be kneaded is made to flow between the kneading bladesof both screws and between the kneading blades having the normal helicaldirection and the kneading blades having the opposite helical direction.FIG. 2 is a sectional view taken along the line II-II of FIG. 1. FIG. 2shows the state in which a material 11 to be kneaded is kneaded in theclearance between the inner wall of the chamber 8 and the kneadingblades 10. Three chip kneading blades 10 are provided along theperiphery of each screw shaft with an angle of 120° therebetween andwith a bite angle α. Additionally, the midpoint in which the helicaldirection is reversed is not necessarily located in the exact middle ofthe kneading blade section, and the midpoint may be placed in thedownstream side in the extrusion process so as to accelerate thetransport of the material to be kneaded.

With respect to the structure of the chamber 8, as shown in FIG. 2, twocylindrical passages in which a pair of screws rotate are placed inparallel and are connected to each other. The barrel 9 is constructed soas to form the chamber 8. The barrel 9 is composed of detachable units,each unit being a screw section or a kneading blade section. This isbecause the barrel 9 is designed so that various combinations of thescrew sections and the kneading blade sections can be selected or thenumbers of the injecting devices and the discharging devices can beappropriately selected.

Additionally, a cooling jacket for passing a cooling medium may beinternally or externally provided on at least one unit constituting thebarrel 9.

A rubber feed port 12 for feeding a rubber-based composition into thechamber 8 is provided on the first screw section 7 a located upstream inthe twin-screw kneading extruder 1. As shown in FIG. 1, the rubbermetering feeder 2 having a twin screw extruding device is connected tothe rubber feed port 12. The raw materials of a rubber-based compositionare continuously fed into the chamber 8 by the twin-screw extrudingdevice. The rubber metering feeder 2 allows continuous feed of the rawmaterial rubber at a constant rate regardless of the form of the rawmaterial rubber, i.e., the raw material rubber may be in the form ofpowder or in a lump. Additionally, the rubber metering feeder 2 does notnecessarily include a twin-screw extruding device, and the rubbermetering feeder 2 may include a single-screw extruding device, amulti-screw extruding device having more than three screws, or a gearpump. In either case, continuous feed can be performed at a constantrate regardless of the form of the raw material rubber.

In the twin-screw kneading extruder 1, the injection pumps 3 and 4 areconnected to injection ports 13 and 14 provided on the barrel at thepositions where the second kneading blade section 7 d and the thirdkneading blade section 7 f are placed, respectively. These elementsconstitute the injecting devices. Water sent from the injection pumps 3and 4 is injected into the chamber 8 through the injection ports 13 and14, and the material to be kneaded and the water are mixed together.Thereby, heat generated from the material to be kneaded can be removed.

The vacuum pumps 5 and 6 are connected to suction ports 15 and 16provided on the barrel at the positions where the third screw section 7e and the fourth screw section 7 g are placed, respectively. The chamber8 can be evacuated by suction in the regions where the third screwsection 7 e and the fourth screw section 7 g are placed by the vacuumpumps 5 and 6. Since the pressure is reduced as described above, waterinjected in the second screw section 7 d and the third screw section 7 fand contained in the material to be kneaded is vaporized and is suckedout by the vacuum pumps 5 and 6.

An injecting device is provided in the second kneading blade section 7 dfirst because a high-temperature state which requires cooling is notbrought about in the first kneading blade section 7 b and because it maybe necessary to accelerate the heat generation of the rubber-basedmaterial to a certain extent so that the rubber-based material isplasticized and the sealing effect is displayed in order to remove waterunder vacuum in the downstream process. In the fourth kneading bladesection 7 h in the last stage, an injecting device is not providedbecause it is not possible to perform dewatering by vacuum in thedownstream side. In the meantime, when a rubber-based composition fedinto the twin-screw kneading extruder 1 has a high temperature, sincethe rubber-based composition can display the sealing effect in the firstkneading blade section 7 b, it is possible to inject water in the firstkneading blade section 7 b and to evacuate by suction in the unitbetween the first kneading blade section 7 b and the second kneadingblade section 7 d.

Moreover, when a cooling jacket for passing a cooling medium isprovided, since indirect cooling is performed in addition to directcooling by the injection of water, the removal of heat can be moreeffectively performed from a material to be kneaded which generatesheat.

Additionally, the numbers of the kneading blade sections and the screwsections are not limited to this embodiment, and are preferably selectedappropriately depending on the quality of the rubber-based compositionto be processed and the desired decreased value of viscosity. Thenumbers and positions of the injecting devices and the dischargingdevices are also not limited to this embodiment.

Next, the operation of the kneading apparatus for rubber-basedcompositions in the first embodiment of the present invention will bedescribed step by step in the process of producing a kneadedrubber-based composition. First, raw materials for a rubber-basedcomposition including a filler, such as carbon black, and variouscompounding ingredients in various forms of powder, lump, or sheet arefed into the rubber metering feeder 2. The raw material rubber fed intothe rubber metering feeder 2 is transported to the feed port 12 of thetwin-screw kneading extruder 1 at a constant rate by the twin-screwextruding device constituting the rubber metering feeder 2.

The raw material rubber fed into the twin-screw kneading extruder 1 at aconstant rate through the feed port 12 is delivered to the chamber 8 atthe position where the first screw section 7 a is located. At thisstage, the screw assembly 7 (a pair of screws) is already being rotatedby a driving device (not shown in the drawing). The rubber-basedcomposition as the material to be kneaded is extruded to the firstkneading blade section 7 b by the rotating helical blades of the screwsection 7 a. In the first kneading blade section 7 b, the material to bekneaded starts to fill between the inner wall of the chamber 8 and thekneading blades, and the material to be kneaded is made to flow and ismixed and dispersed in the clearance between the inner wall of thechamber 8 and the kneading blades while being applied with shearingforces, and thus kneading is performed.

The material kneaded in the first kneading blade section 7 b moves tothe second screw section 7 c by being extruded by the material fillingthe upstream side. The material moved to the second screw section 7 c istransported to the second kneading blade section 7 d by the rotation ofthe helical blades.

The material transported to the second kneading blade section 7 d iskneaded again in the same manner as the first kneading blade section 7 bapart from the fact that water sent from the injection pump 3 isinjected into the second kneading blade section 7 d through theinjection port 13. Consequently, the material to be kneaded is broughtinto contact with water during kneading. At this stage, the temperatureof the material to be kneaded is increased to a certain extent due tothe heat generation during kneading in the first kneading blade section7 b, and the temperature is further increased because heat generationoccurs during kneading in the second kneading blade section 7 d.However, since the water injected is mixed with the material to bekneaded and is brought into sufficient contact with the material to bekneaded, heat can be removed from the material to be kneaded.

The material to be kneaded thus cooled by the injection of water isextruded to the third screw section 7 e by the material moved from theupstream side into the second kneading blade section 7 d. In the thirdscrew section 7 e, the material to be kneaded is transported in the samemanner as the upstream screw section apart from the fact that theatmospheric gas in the chamber 8 is sucked out by the vacuum pump 5through the suction port 15 and a reduced-pressure space is produced. Atthis stage, the materials filled in the adjacent kneading blade sectionsdisplay the sealing effect to secure the reduced-pressure space.Alternatively, as described above, the helical blades in the upstreamend and the downstream end in the third screw section 7 e may be denselypitched in the axial direction and the helical blades at the positioncorresponding to the suction port 15 may be sparsely pitched so that thematerial to be kneaded fills the densely pitched area, therebydisplaying the sealing effect.

Since the chamber 8 in which the third screw section 7 e is evacuated asdescribed above, vaporization and evaporation of the water contained inthe material to be kneaded are accelerated. Since heat of vaporizationof water is large, it is possible to efficiently remove heat from thematerial to be kneaded with the addition of a small amount of water.Accordingly, just water used for cooling is separated and dewatering isappropriately performed, and also both absorption of heat by water andremoval of heat by vaporization are performed, and thereby cooling canbe performed efficiently.

The material to be kneaded in which water is removed in the third screwsection 7 e is transported to the third kneading blade section 7 f. Inthe third kneading blade section 7 f, kneading is performed whileinjecting water again for cooling in the same manner as the secondkneading blade section 7 d. Furthermore, in the fourth screw section 7g, water is removed in the same manner as the third screw section 7 e.The material to be kneaded is then transported to the fourth kneadingblade section 7 h which is the final stage, and just kneading isperformed therein, and then the material is extruded as a lump from thefront end into the air.

It is to be understood that the embodiment described above also coversthe method for kneading rubber-based compositions in accordance with thepresent invention.

A kneading apparatus for rubber-based compositions in a secondembodiment of the present invention will now be described. FIG. 3 is aschematic sectional view of the kneading apparatus in this embodiment.As shown in FIG. 3, the kneading apparatus includes a twin-screwkneading extruder 1, and a rubber metering feeder 2, injection pumps 3and 4, and a vacuum pump 5 connected to the twin-screw kneading extruder1. The twin-screw kneading extruder 1 includes a screw assembly 7, achamber 8, and a barrel 9. The screw assembly 7 has three screw sectionsand three kneading blade sections which are placed alternately. In thesecond embodiment, the injection pumps 3 and 4 are connected to a firstscrew section 7 a and a second kneading blade section 7 d throughinjection ports 13 and 14, respectively, and the injection pump 5 isconnected to a third screw section 7 e through a suction port 15. Thebarrel in the region where the first screw section 7 a is located isprovided with a slit portion 17. In the slit portion 17, slits areformed so as to connect the interior of the chamber 8 to the exterior ofthe chamber 8.

The kneading apparatus in this embodiment has a structure which iseffective in kneading high-temperature raw material rubber directly bythe twin-screw kneading extruder. The characteristic operation of thekneading apparatus will be described below.

For example, a rubber-based composition which has been kneaded to acertain extent by a batch-type mixer or the like and which has a hightemperature is fed into the rubber metering feeder 2. This process isperformed, for example, when there is a difficulty in feeding at aconstant rate unless the raw material rubber is heated to a temperaturethat allows plasticization, or in order to omit the step of cooling hightemperature rubber. The fed material to be kneaded is transported to thedownstream side by the first screw section 7 a, and at this stage wateris injected from the injection pump 3 into the chamber 8 through theinjection port 13. Thereby, the high temperature material to be kneadedbeing transported is brought into contact with water and cooled. Thewater which comes into contact with water and absorbs heat flows in thechamber 8 and is discharged from the slit portion 17. By appropriatelysetting the width of slits in the slit portion 17, it is possible tojust discharge water used for cooling without discharging the materialto be kneaded from the chamber 8. Even when a large amount of coolingwater is required, it is possible to efficiently remove the water, and adewatering device can be produced with a simple construction.

Since the material to be kneaded cooled in the first screw section 7 ais processed afterward in the same manner as the first embodiment, thedescription thereof will be omitted. The numbers of the screw sectionsand the kneading blade sections and the numbers of the injecting devicesand the discharging devices are not limited to this embodiment and canbe appropriately selected depending on the quality of the rubber-basedcomposition to be processed, the desired reduction value of viscosity,etc.

A kneading apparatus for rubber-based compositions in a third embodimentof the present invention will now be described. FIG. 4 is a schematicsectional view which shows a part of a kneading apparatus in the thirdembodiment of the present invention, taken along the shafts of a screwassembly 7. The kneading apparatus in this embodiment is the same as thefirst embodiment apart from the fact that a gate device 18, which is agap-adjusting device, is provided between the second kneading bladesection 7 d and the third screw section 7 e. FIG. 5 is a sectional viewof the gate device 18, perpendicular to the shafts of the screw assembly7. The gate device 18 includes two gates 19 located so as to sandwichthe screw assembly 7, and the gates 19 are provided perpendicularly tothe shafts of the screw assembly 7 and so as to be movable in relationto the screw assembly 7. Thereby, a gap formed between the screwassembly 7 and the gate 19, i.e., the area through which the material tobe kneaded passes, can be adjusted. By changing the gap, the extrudedmaterial to be kneaded is squeezed and the flow resistance of thematerial to be kneaded is changed, and thus the material residence timein the kneading apparatus can be adjusted. That is, it is possible toadjust the filling factor of the material to be kneaded in the kneadingblade section, and desired kneading conditions can be easily adjusted.Additionally, the gate device 18 is not limited to the example describedabove. Gate devices may be provided in a plurality of kneading bladesections and screw sections. A gate device may be composed of two gaterods sandwiching the screw assembly 7, each rotating without movingperpendicularly. A gate device may have a structure including a conicalpart provided on the screw assembly 7 and a slot formed between theconical part and the chamber, in which the chamber and the conical partare relatively moved in the axial direction of the screw assembly 7.Alternatively, a pin type gate device may be used, such as the one seenin a rubber extruder.

A kneading apparatus for rubber-based compositions in a fourthembodiment of the present invention will now be described. FIG. 6 is aschematic diagram showing a kneading apparatus in this embodiment. Thekneading apparatus is the same as the first embodiment apart from thefact that temperature-measuring sections 20 a and 20 b for measuring thetemperature of the material to be kneaded are provided in the secondkneading blade section 7 d and the third kneading blade section 7 f.Furthermore, the kneading apparatus includes a control section forcontrolling the amount of water to be injected into the chamber 8 andthe speed of rotation of the screw assembly 7 based on the temperaturesmeasured, and an input section for transmitting the values measured bythe temperature-measuring sections 20 a and 20 b.

If the speed of rotation of the screw assembly 7 is increased, thekneading power is increased. Therefore, high speed revolution isdesirable in view of kneading efficiency. However, as the speed ofrevolution is increased, the amount of heat generated from the materialto be kneaded is increased. The heat generated from the material to bekneaded varies depending on the type of rubber-based compositions to bekneaded, the viscosity of the material during kneading, etc. Therefore,the screw assembly 7 is desirably rotated as fast as possible whilemonitoring the heat-generating state and appropriately adjusting thecooling capability so that the temperature of the material to be kneadedis properly maintained.

In this embodiment, based on the temperatures measured in the kneadblade sections 7 d and 7 f, the control section determines the amount ofwater injection necessary for keeping the material to be kneaded at adesired temperature, and the highest possible speed of rotation underthe temperature and the amount of water injection, and the controlsection then prepares operational instructions for the injection pumps 3and 4 as well as a driving motor 21 of the screw assembly 7. Followingthe operational instructions, the injection pumps 3 and 4 and thedriving motor 21 are operated. Thereby, it is possible to achieve thefastest and most efficient kneading conditions in response to theheat-generating state which changes during kneading.

It is to be understood that the present invention is not limited to theindividual embodiments described above. For example, the embodiments maybe modified as follows.

(1) The rubber metering feeder does not necessarily include a screwextruding device or a gear pump. For example, as in a kneading apparatusfor rubber-based compositions shown in FIG. 7, a device for feeding rawmaterial rubber in the form of sheet or ribbon may be used, in which asheet/ribbon rubber 23 as a raw material is directly fed to the feedport 12 from a sheet/ribbon stock 22 by a guide roller 24. When adirectly connected rubber metering feeder, such as a screw extrudingtype, is used, if the temperature of the raw material rubber to be fedinto the twin-screw kneading extruder is not increased sufficiently forplasticization, the constant feed accuracy is decreased, resulting invariations in the kneaded material. Therefore, when a directly connectedrubber metering feeder is used, the raw material rubber must be heatedto a certain extent, and as a result, with respect to the rubber fedinto the twin-screw extruder which preferably has a low temperature, anincrease in temperature to a certain extent is unavoidable. However, inaccordance with the modified example described above, since it ispossible to continuously feed the sheet/ribbon rubber 24 at a constantrate while keeping the low temperature, low temperature kneading isfurther ensured.

(2) Various compounding ingredients to be mixed with raw material rubberare added to and mixed with the raw material rubber by a batch-typekneader before being kneaded in the kneading apparatus for rubber-basedcompositions. However, as shown in FIG. 7, a feed port 25 for feedingvarious liquid compounding ingredients directly into the barrel intowhich raw material rubber is fed may be provided. Thereby, it ispossible to knead various compounding ingredients by the twin-screwkneading extruder while feeding the compounding ingredientssimultaneously with raw material rubber without preliminarily mixing thecompounding ingredients by a batch-type kneader. In such a case, thekneading apparatus can be also used in the final step in addition to inthe remilling step. When various compounding ingredients in the form ofpowders are added, as shown in FIG. 8, a hopper 26 may be provided onthe kneading apparatus so that the various compounding ingredients arefed together with raw material rubber. In such a case, preferably, ametering feeder used for the various compounding ingredients which issimilar to the rubber metering feeder is also connected the kneadingapparatus.

(3) A sheet forming device may be provided on the front end of thetwin-screw kneading extruder as shown in FIG. 7. The sheet formingdevice includes an extrusion die 27 and a roller head 28 connected tothe front end of the twin-screw kneading extruder. Consequently, sheetforming can be performed directly at the front end of the extruder, andby forming a sheet of the kneaded material, cooling is accelerated andhandling in the subsequent step is facilitated.

(4) With respect to the direction of rotation of the screw assembly,twin screws are not always required to rotate in the same direction. Thetwin screws may have helical blades so as to extrude the material to bekneaded by rotating in the different directions.

(5) The kneading blade section does not necessarily have three blades asdescribed in the above embodiment. The kneading blade section may becomposed of one blade or two blades. Alternatively, the kneading bladesection may be composed of a plurality of kneading disks.

(6) The dewatering device may have a mechanism in which dewatering isperformed by evaporation due to exposure to air. Thereby, power savingscan be achieved. In such a case, it is also possible to remove waterwhile preventing the leakage of the material reliably.

(7) The kneading extruder is not necessarily of a twin-screw type, andfor example, a single-screw kneading extruder may be used.

EXAMPLES

The present invention will be described more specifically based on theexamples. However, it is to be understood that the present invention isnot limited to the examples.

Testing was performed using the kneading apparatus in accordance withthe first embodiment with a twin-screw kneading extruder having a screwdiameter of 59 mm. Cooling water at a temperature of 20° C. was injectedby the injection pump. The rubber-based composition used as a rawmaterial had a Mooney viscosity (100° C.) of 100, and it wascontinuously fed from the rubber metering feeder in which thetemperature was adjusted to 60° C. The raw material rubber was fed at arate of 50 kg/hr and at a rate of 100 kg/hr. Kneading was performed byvarying the water-injecting conditions and the speed of rotation of thetwin-screw kneading extruder, and then the temperature of the kneadedmaterial at the discharge port of the extruder, a decrease in the Mooneyviscosity, and the energy required to perform kneading were measured.The barrel was indirectly cooled by passing cooling water of 20° C. Theresults thereof are shown in Table 1.

TABLE 1 Rotation speed of Decrease in Rubber twin- Temperature viscosityfeeding screw of rubber (Mooney rate Water extruder discharged viscosityEnergy (kg/hr) injection (rpm) (° C.) 100° C.) (kWh/kg) Comparative 50No 120 161 19 points 0.58 Example injection Example 1 50 7% 120 123 30points 0.63 injection (3.5% × 2 spots) Example 2 50 7% 250 173 30 points0.79 injection (3.5% × 2 spots) Example 3 50 14% 250 154 36 points 0.72injection (7% × 2 spots)

First, testing performed at a rubber feeding rate of 50 kg/hr will bedescribed. When Example 1 is compared to Comparative Example in which nowater injection was performed but with the same rotation speed,obviously, by injecting water, the temperature can be decreased to alevel considerably lower than 160° C. which is considered to be theupper limit for the degradation of rubber physical properties. Theviscosity is also decreased considerably. This is because thetemperature of the rubber is decreased by water cooling and lowtemperature kneading enables efficient mechanical shearing. The above isalso supported by the fact that the amount of energy required to performkneading is large.

When Example 2 is compared to Example 3 in which the amount of waterinjected was increased to 14% with the same rotation speed, it has beenfound that the energy required to perform kneading is decreased due toan increase in the amount of water injected. Since a large amount ofwater is injected, it is believed that slipping of rubber often occursin the kneading chamber. Testing was also conducted in other examplesnot shown in Table 1, and as a result, the energy required to performkneading generally increased up to an injection of several to severalten percent, and at the amount of injection higher than that, the energymaintained equilibrium or decreased. In the slipping region at aninjection of 10% or more, rubber was discharged at low temperatures, thedecrease in viscosity was large, and thus kneading was considered to beperformed efficiently with low energy. However, water injected was notvaporized sufficiently, water in the liquid state was partially suckedout by the vacuum pump, and rubber was also sucked out together withwater. Therefore, operation must be performed at the appropriate upperlimit of water injection depending on the evacuating capability, thevolume of the chamber, etc.

Although the testing results at a rubber feeding rate of 100 kg/hr werenot shown in Table 1, the decrease in temperature and the decrease inviscosity due to the injection of water were observed in the same manneras the case at the rate of 50 kg/hr. It has also been found that energyrequired to perform kneading decreases as the amount of water injectedincreases in the same manner as the case at the rate of 50 kg/hr.

Consequently, it has been confirmed that, in accordance with the presentinvention, it is possible to provide a kneading apparatus forrubber-based compositions having high viscosities in which continuouskneading treatment can be performed without repeated remilling, thusgreatly improving productivity, and to provide a kneading method usingthe kneading apparatus. Additionally, the effects of the examplesdescribed above can also be obtained in any embodiment of the presentinvention and the modifications thereof.

1. A method of kneading a rubber-based composition comprising rubber andcompounding ingredients using a kneading apparatus comprising a barrelhaving a cylindrical chamber; a screw assembly rotating in the chamberfor extruding a material to be kneaded in the axial direction, saidscrew assembly comprising a screw section having helical blades and akneading blade section for allowing the material to flow into theclearance between the inner wall of the chamber and a kneading blade ofsaid kneading blade section, and for applying shearing forces to thematerial to be kneaded; a metering feeder for feeding the material at asubstantially constant volumetric rate or at a substantially constantgravimetric rate from a feed port provided on the barrel into thechamber; an injecting device provided on the barrel for injecting aheat-removing medium into the chamber; a dewatering device thatseparates the heat-removing medium in a liquid state from the materialby subjecting the rubber-based composition to a filling and compressingaction; and a discharging device for separating the heat-removing mediumin a vapor state from the material, wherein the heat-removing medium hasbeen injected into the chamber by said injecting device and mixed withthe material, and discharging the heat-removing medium from the chamber,the method comprising: a feeding step of feeding the rubber-basedcomposition into the chamber of the kneading apparatus at asubstantially constant volumetric rate or at a substantially constantgravimetric rate by the metering feeder, wherein the rubber-basedcomposition has a Mooney viscosity at 100° C. of not less than 100; akneading step of allowing the rubber-based composition to flow into theclearance between the inner wall of the chamber and the kneading bladesection and moving the rubber-based composition in the chamber whilemixing and dispersing the rubber-based composition by means of shearingforces; a mixing step of injecting a liquid heat-removing medium intothe chamber by the injecting device and mixing the rubber-basedcomposition with the heat-removing medium before or during kneading,sufficient to maintain the temperature of the rubber-based compositionat 160° C. or less during kneading; a dewatering step of separating theheat-removing medium in a liquid state from the rubber-based compositionby the dewatering device by subjecting the rubber-based composition to afilling and compressing action; and a discharging step of dischargingthe separated heat-removing medium in a vapor state by the dischargingdevice provided at the location in the axial direction of the dewateringdevice.
 2. The method for kneading a rubber-based composition accordingto claim 1, wherein the heat-removing medium is water.
 3. The method forkneading a rubber-based composition according to claim 1, wherein thedischarging device is a vacuum pump connected to the chamber forevacuating the chamber in the region in which said screw section isplaced.